Crystal growth and superconductivity of LiTi2O4 and Li1+1/3Ti2-1/3O4

Single crystals of Li1+xTi2-xO4 (x = 0-1/3) and LiTi2O4 are grown by using binary eutectic fluxes and by molten salt electrocrystallisation, respectively. LiTi2O4 crystals show a sharp superconducting transition width of 0.1 K at T-c = 11.3 K by AC susceptibility measurement, while Li1+1/3Ti2-1/3O4 is semiconducting down to liquid helium temperature. In contrast to the instability of polycrystalline sample, the high quality single crystals are very stable in ambient atmosphere. X-ray powder patterns for three spinel crystals in this series are very similar both in positions of the diffraction lines and in the line intensities as well. The cubic cell parameter, a(0) (Angstrom), smoothly decreases as the composition x increases. A narrow metal-semiconductor phase transition at a(0) similar to 8.39 Angstrom is induced by the composition at x similar to 0.07. AC susceptibility measurement is used to study the decomposition kinetics of LiTi2O4 crystals, which occurs in air around 400degreesC. The decomposition reaction follows the first-order kinetic with the activation energy E = 45 kcal/mol and the frequency factor k(0) = 3.9 x 10(8) (1/s). (C) 2002 Elsevier Science B.V. All rights reserved.